The Commission Internationale de l'Éclairage (hereinafter “CIE”) XYZ observer functions are the basis for most color measurements that require the matching of colors. By combining these functions with non-linear color appearance models (CAMs) such as CIELAB and CIECAM96s CAMs, complex color images as well as simple color patches can be reproduced with great success.
The CIELAB model for example is reasonably effective in predicting the appearance of hue for colors ranging from near neutral to regions of high saturation with the exception of regions of extremely saturated blue color. For example, saturated blue images on computer displays will appear extremely purple if converted to CMYK printed images even though CIELAB measurements would indicate nearly identical values of hue. This phenomenon was documented by Hung and Berns in their paper “Determination of constant hue loci for a CRT gamut and their predictions using color appearance spaces”, P. C. Hung and R. S. Berns, Color Res. Appl. 20, 285-295 (1995) and is therefore often referred to as the Hung-Berns effect.
Plots shown by Hung-Berns indicate a hue shift in blue that equates to 30 ΔE or more. Until now, this phenomenon has not been well understood and has been corrected using empirical spline corrections or similar techniques that at times do not provide for optimal correction. A need thus exists for characterizing and correcting for the effects of hue shifts in saturated colors, in particular blue colors, such as for example when performing color conversions from RGB images containing saturated blue and CMYK prints which are attempting to reproduce those RGB images.